[Info-vax] LTFS

[Glenn Everhart]

Tape based filesystems on VMS are of course not new (seeing that one is natively supported by
MTAACP even in RSX, with VMS descendants.)

If you want to play with access, there's a system I put on the sigtapes some time back
that will let you make a BACKUP/PHYSICAL of a disk and present the result to you as a
disk (using a driver I called DTdriver, for old time's sake). It caches some of the tape
blocks and tries to move around quickly.

It is however read-only and will demonstrate to you that as an everyday technique of accessing
storage it leaves much to be desired. Transfer times are OK, but seek times are the killer.

I imagine LTFS must keep some access information on disk so it can find things more
quickly than linear search, and may play some of the kinds of version tricks that will
write new file versions on the end of the tape, to avoid figuring out a way to erase
old ones.

The kind of thing my hack was designed for was creation of faster backups, while still
allowing partial retrieval. That works fine, with performance limitations. That does
not sound like something you'd want to use all the time, and if you try using it to access
two large files at once, good luck.
Glenn Everhart